'Quambo' apparently means 'bad' in American slang, but of course that can now mean 'good', can't it? One meaning of 'piece of cake' - apart from an actual piece of cake - is that something is easy, so you can now put the two parts together in whatever way suits you! Is it a foul-tasting bit of baked goods or something that is excellent and easy. (I have no idea where it originated.)